16: The bison are everywhere. We had to almost push them out of the way on our way out of Jackson Hole.

17: The Grand Tetons

18: Canyon Village

26: Rachel; John; Rebekah; Zach, John, Joel

27: Mt. Washburn is a fire lookout located in the north central portion of the park and sits at an elevation of 10,243 feet. Workers live in a tiny tower surrounded by glass for months at a time looking for fires. | Si | John, Joel, Si | Joel

32: Old Faithful Geyser

33: Old Faithful was named by the first official expedition to Yellowstone, the Washburn Expedition of 1870. They were impressed by its size and frequency. Old Faithful erupts every 35 to 120 minutes for 1 .5 to 5 minutes. Its maximum height ranges from 90 to 184 feet.

34: Dragon's Mouth Spring | An unknown park visitor named this feature around 1912, perhaps due to the water that frequently surged from the cave like lashing of a dragon's tongue. Until 1994, this dramatic wave-like action often splashed water as far as the boardwalk. The rumbling sounds are caused by steam and other gases exploding through the water, causing it to crash against the walls of the hidden cavern. | Ben, Beck, Rachel, Ab, Zach

35: When the Washburn Expedition explored the area in 1870, Nathaniel Langford described Mud Volcano as "greatest marvel we have yet met with." Although the Mud Volcano can no longer be heard from a mile away nor does it throw mud from its massive crater, the area is still eerily intriguing. The short loop from the parking lot past the Dragon's Mouth and the Mud Volcano is handicapped accessible. The half-mile upper loop trail via Sour Lake and the Black Dragon's Caldron is relatively steep. Two of the most popular features in the Mud Volcano front country are the Dragon's Mouth and the Black Dragon's Caldron. The rhythmic belching of steam and the flashing tongue of water give the Dragon's Mouth Spring its name, though its activity has decreased notably since December 1994. The Black Dragon's Caldron exploded onto the landscape in 1948, blowing trees out by their roots and covering the surrounding forest with mud. The large roil in one end of the Caldron gives one the sense that the Black Dragon itself might rear its head at any time. In January 1995, a new feature on the south bank of Mud Geyser became extremely active. It covers an area of 20 by 8 feet and is comprised of fumaroles, small pools, and frying-pan type features. Much of the hillside to the south and southwest of Mud Geyser is steaming and hissing with a few mudpots intermixed. This increase in activity precipitated a great deal of visitor interest and subsequent illegal entry into the area. The most dramatic features of the Mud Volcano area however, are not open to the public. The huge seething mud pot known as the "Gumper" is located off-boardwalk behind Sour Lake. The more recent features just south of the Gumper are some of the hottest and most active in the area. Ranger-guided walks are offered to provide visitors an opportunity to view this interesting place. Farther in the backcountry behind Mud Volcano, several features are being tested for the existence of thermophilic microbes, which may offer insights into origin of life theories as well as having medical/environmental applications.

40: Old Faithful Geyser Giantess Geyser Doublet Pool Solitary Geyser Observation Point Plume Geyser Beehive Geyser Heart Spring Lion Group of Geysers Sawmill Geyser Grand Geyser Crested Pool Castle Geyser Beauty Pool Chromatic Spring Giant Geyser Comet Geyser Splendid Geyser Punch Bowl Spring Daisy Geyser Grotto Geyser Riverside Geyser Fan & Mortar Geysers Morning Glory Pool Biscuit Basin Sapphire Pool | Sprinkled amid the hot springs are the rarest fountains of all, the geysers. What makes them rare and distinguishes them from hot springs is that somewhere, usually near the surface in the plumbing system of a geyser, there are one or more constrictions. Expanding steam bubbles generated from the rising hot water build up behind these constrictions, ultimately squeezing through the narrow passageways and forcing the water above to overflow from the geyser. The release of water at the surface prompts a sudden decline in pressure of the hotter waters at great depth, triggering a violent chain reaction of tremendous steam explosions in which the volume of rising, now boiling, water expands 1,500 times or more. This expanding body of boiling superheated water bursts into the sky as one of Yellowstone’s many famous geysers. There are more geysers here than anywhere else on earth. Old Faithful, certainly the most famous geyser, is joined by numerous others big and small, named and unnamed. Though born of the same water and rock, what is enchanting is how differently they play in the sky. Riverside Geyser shoots at an angle across the Firehole River, often forming a rainbow in its mist. Castle erupts from a cone shaped like the ruins of some medieval fortress. Grand explodes in a series of powerful bursts, towering above the surrounding trees. Echinus spouts up and out to all sides like a fireworks display of water. And Steamboat, the largest in the world, pulsates like a massive steam engine in a rare, but remarkably memorable eruption, reaching heights of 300 to 400 feet.

43: Yellowstone Lake

44: Zach | Ben

45: Ben | Joel

47: Obsidian Cliff 11 miles south of Mammoth Hot Springs, is at the northern end of Beaver Lake in Yellowstone National Park. The cliff forms the eastern wall of a narrow cut in plateau country. At an elevation of nearly 7,400 feet above sea level, the cliff extends for a half mile, rising from 150 to 200 feet above Obsidian Creek and falling gradually away to the north. The upper half is a vertical face of rock; the lower half is composed of loose and broken rocks forming a talus slope. The cliff is the remainder of a flow of lava that erupted onto the earth's surface and then poured down the plateau. Obsidian forms when lava cools so quickly that crystals do not have time to form and grow. Because obsidian is usually found as small globes in other rocks, a massive outcrop the size of Obsidian Cliff is quite rare. Obsidian Cliff possibly formed when molten rock (magma) erupted onto the earth's surface and came into contact with the ice of a glacier. This quick cooling of large amounts of magma prevented the growth of crystals. Also, chemical analyses of the obsidian show that there was very little water in the lava. Without water, crystals could not form, thereby resulting in glassy rock. On close observation, one can see the swirling flow in the rock that shows the last movement of the liquid magma before it cooled and hardened. Found on the southern face of the cliff are a series of columns which commonly occur in rocks of volcanic origin. Columnar jointing, as this formation is called, is another result of the rapid cooling of magma. The liquid rock shrinks inward, cracks, and contracts as it cools to form these four-to-six sided columns. For centuries, Native Americans made their arrowheads and spear points from obsidian. The rock itself is dark and glassy in appearance (black in this case), and, when broken, fractures into rounded pieces with sharp edges. Arrowheads from as far away as the Midwest have had their origin traced back to Obsidian Cliff in Yellowstone. This indicates that the quality of obsidian found here was great enough for it to spread long distances in its use among various Indian tribes.

48: Si, John, Ben, Beck, Zach, Rach, Joel | Rach, Joel, Ab

51: Si, Ben

53: Beck, Si, Rach, Joel

54: Grand Prismatic Spring Grand Prismatic Spring, located in Midway Geyser Basin, has the distinction of being the park’s largest hot spring. It measures approximately 370 feet (112.8 m) in diameter and is over 121 feet (37 m) deep. A description of this spring by fur trapper Osborne Russell in 1839 also makes it the earliest described thermal feature in Yellowstone that is definitely identifiable.

56: Fairy Falls

58: Si and Ben's Adventure-to the top of fairy falls then out the other side to an unnamed lake, possibly Goose Lake. This nearly required park ranger assistance.

60: Joel, Rach | Ab, Beck | Rach, Ab

62: Lamar Valley

66: Mammoth Hot Springs Terraces

67: Several key ingredients combine to make the Mammoth Hot Springs Terraces: heat, water, limestone, and a rock fracture system through which hot water can reach the earth's surface. Today's geothermal activity is a link to past volcanism. A partially molten magma chamber, remnant of a cataclysmic volcanic explosion 600,000 years ago in central Yellowstone, supplies one of the ingredients, heat. Hot water is the creative force of the terraces. Without it, terrace growth ceases and color vanishes. The source of the water flowing out of Yellowstone's geothermal features is rain and snow. Falling high on the slopes in and around Yellowstone, water seeps deep into the earth. This cold ground water is warmed by heat radiating from the magma chamber before rising back to the surface. Hot water must be able to reach the earth's surface in relatively large volumes to erupt as a geyser or flow as a hot spring. In Yellowstone, many conduits remain from the collapse of the giant caldera; frequent earthquakes keep this underground "plumbing" system open. Even though Mammoth lies north of the caldera ring-fracture system, a fault trending north from Norris Geyser Basin, 21 miles (34 km) away, may connect Mammoth to the hot water of that system. A system of small fissures carries water upward to create approximately 50 hot springs in the Mammoth Hot Springs area. Another necessary ingredient for terrace growth is the mineral calcium carbonate. Thick layers of sedimentary limestone, deposited millions of years ago by vast seas, lie beneath the Mammoth area. As ground water seeps slowly downward and laterally, it comes in contact with hot gases charged with carbon dioxide rising from the magma chamber. Some carbon dioxide is readily dissolved in the hot water to form a weak carbonic acid solution. This hot, acidic solution dissolves great quantities of limestone as it works up through the rock layers to the surface hot springs. Once exposed to the open air, some of the carbon dioxide escapes from solution. As this happens, limestone can no longer remain in solution. A solid mineral reforms and is deposited as the travertine that forms the terraces.